Pressure forming apparatus



Nov. 13, 1962 3,063,098

H. EYBERGER PRESSURE FORMING APPARATUS Filed May 17, 1957 4 Sheets-Sheetl "/3\ x%p 28L 3, As, 1 z

FIG 2 INVENTOR HARRY E YBE R65 R ATTORNEYS Nov. 13, 1962 H. EYBERGERPRESSURE FORMING APPARATUS Filed May 1'7, 195? 4 Sheets-Sheet 2 INVENTORHARRY KYBERGER mam ATTORNEYS Nov. 13, 1962 H. EYBERGER 3,063,098

PRESSURE FORMING APPARATUS Filed May 17, 1957 4 Sheets-Sheet s 1N VENTOR 4? H41? E RGER F/6Z8 l ATTORNEYS Nov. 13, 1962 v H. EYBERGER3,063,098

PRESSURE FORMING APPARATUS Filed May 17, 1957 4 Sheets-Sheet 4 INVENT ORHARRY EYBERGER R ATTORNEYS United States Patent 3,063,098 PRESSUREFORMING APPARATUS Harry Eyberger, Butler, Pa., assignor to Magnetics,Inc., a corporation of Pennsylvania Filed May 17, 1957, Ser. No. 659,925Claims. (Cl. 18-42) This invention relates to the formation of bodies ofcompressed metallic particles, such as magnetic bodies of compressedinsulated particles of magnetic material. In particular, the inventionrelates to novel apparatus for forming integral bodies from powderedmetallic material, including insulated particles of magnetic material,under high pressure, and to a novel magnetic body formed of compressedparticles of magnetic material having improved magnetic, electrical andmechanical characteristics.

The formation of certain bodies of compressed metallic particles, suchas the formation of toroidal magnetic cores of compressed insulatedparticles of magnetic material,

requires application of extremely high pressures, such as.

200,000 to 250,000 pounds per square inch. For this operation, a moldingdie is employed presenting a pressure or molding cavity of toroidalshape, for example, into which a measured quantity of powdered material,such as insulated particles of magnetic material, is deposited. Apressure ring is placed in the cavity over the charge of powderedmaterial and the required pressure is applied through the pressure ringto form the powdered material into an integral body of a shapetheoretically determined by the configuration of the pressure cavity. Inview of the high pressures required, it has been necessary in the pastto employ a molding die made up of a plurality of removable arcuate diesections in order to permit withdrawal of the formed body from thepressure cavity. Or dinarily, three arcuate die sections have beenemployed to form a sectional ring about a center plug with a pressurecavity therebetween, the outer and inner contour of the pressure cavitybeing defined by the innermost surfaces of the die sections and thecenter plug, respectively. The arcuate die sections are positivelyclamped, on a suitable platform or table about the center plug inend-to-end relation to form the cavity, and after the required pressureis applied to the charge of powdered material through the pressure ring,the die sections are unclamped from the platform and moved away from theformed body to permit the body to be removed from the center plug. Thenecessity of unclamping the die sections to permit removal of a formedbody and of reclamping the die sections in proper relation with thecenter plug before forsections has made it impractical to form bodies'ofcom pressed powdered material in an automatic operation.

When the required forming-pressure is applied to a charge of powderedmaterial in a cavity of a molding die including a plurality of arcuatedie sections, the outer contour of the pressure cavity becomesdistorted, that is, the outer wall of the cavity defined by the diesections flexes outwardly away from the center plug. After the pressureis relieved the die sections return to their original shape causingdistortion or flexure of the formed body. The flexure of the formed bodyimpairs the desired properties of the bodyand establishes undesiredstresses in the body which may even cause the body to crack when the diesections are removed. Although attempts have been made to design thearcuate die sections in such a manner as to permit distortion whileunder pressure and allow the sections to return to their normal shapewhen the pressure is released without, appreciably distorting "ice theouter contour of the pressure cavity, the permitted flexure results inthe formation of a body having nonuniform density characteristics whichimpairs'its magnetic and electrical properties and reduces its strength.

Furthermore, the use of a plurality of arcuate die sections to form theouter contour of the pressure cavity results in the formed body beingsubjected to substantially lower pressures along the dividing linebetween adjacent die sections. The application of substantiallydifferent pressures during formation of the body is believed to resultin further impairment of the desired uniform density characteristics ofthe body and provides a body of non-uniform permeability in cases wheremagnetic material is employed. As a result of the relieved pressurealong the dividing lines between the arcuate die sections, the core hasan outside surface including a number of seams, equal to the number ofdie sections employed, which break the continuity of the skin of thecore and provide regions of non-uniform density. The foregoing impairsthe magnetic, electrical and mechanical properties of the core.

It is an object of the present invention to provide novel apparatuswhich overcome the disadvantages outlined above.

Another object is to provide a novel molding die for forming cores ofhighly compressed metallic particles, such as insulated particles ofmagnetic material, capable of automatic operation.

In general, the present invention provides a novel arrangement forforming integral bodies of compressed powdered material by substantiallyuniformly subjecting powdered material in a pressure cavity torelatively high pressure Without flexure or deformation of the bodyduring the forming process or upon releasing the pressure following theforming process, and of removing bodies of compressed powdered metallicmaterial from a pressure cavity. In particular the present inventionprovides a novel molding die, capable of forming cores in an automaticoperation, having a pressure cavity including an outside continuous orclosed surface formed on a body member comprising a single piece ofmaterial and an inside continuous or closed surface formed on a centerplug or member relatively movable with respect to the body member. Theinside and outside continuous surfaces are formed in predeterminedrelative relationship to permit withdrawal of a formed core from thepressure cavity upon relative movement between the body member and thecenter plug along the longitudinal axis of the formed core. Magneticcores produced by the novel methods and apparatus of the presentinvention are of more uniform density and permeability and possessimproved magnetic, electrical and strength characteristics. In thepreferred form of the invention the inside and outside continuoussurfaces present substantially circular and substantially concentricinner and outer pressure cavity walls which provide more equaldistribution of the forming pressure throughout the body. i

The foregoing and other objects and features of the present inventionwill appear more fully from the following detailed descriptionconsidered in connection with the accompanying drawings which discloseseveral em bodiments of the invention. It is to be expressly understood,however, that the drawings are designed for purposes of illustrationonly and not as a definition of the limits of the invention, referencefor the latter purpose being had to the appended claims.

In the drawings, in which similar reference characters denote similarelements throughout the several views:

FIGURE 1 is a diagrammatic plan view of an automatic machine including aplurality of novel molding dies 7 provided by the present invention;

FIGURE 2 is a view in section taken along the line 22 of FIGURE 1;

FIGURE 3 is a view in section taken along the line 33 of FIGURE 1;

FIGURE 4 is an elevational view, partly in section, illustrating thenovel molding die and pressure ring provided by the present invention;

FIGURE 5 is an elevational view, in section, illustrating the relativeposition of the molding die and pressure ring during a core formingoperation;

FIGURE 6 is an elevational view, in section illustrating the position ofthe molding die relative to core ejecting means;

FIGURE 7 is an elevation view, partly in section, illustrating the coreejecting operation provided by the present invention;

FIGURE 8 is an enlarged fragmentary view, in section, illustratingdetails of the pressure cavity provided by a molding die constructed inaccordance with the principles of the present invention;

FIGURE 9 is an enlarged fragmentary view, in section, illustratinganother embodiment of the present invention;

FIGURE 10 is a view, in section, of a magnetic core during a phase ofits formation according to a core forming method provided by the presentinvention;

FIGURE 11 is an elevational view, in section, of a magnetic coreprovided by the present invention;

FIGURE 12 is a plan View of a magnetic core provided by the presentinvention;

. FIGURE 13 is a view in side elevation of a magnetic core provided bythe present invention, and

FIGURE 14 is a fragmentary view, in section, of another einbodiment ofthe present invention.-

. A machine for automatically producing bodies of compressed metallicparticles, such as insulated particles of magnetic materiaLaccording tothe principles of the present invention is shown in FIGURE 1 of thedrawings included a table 10 mounted for rotation about its center in ahorizontal plane above a support 11. A plurality of molding dies 12 aremounted on the upper surface of the table 10 at equally spaced angularpositions and radial distances with respect to the center of rotation ofthe table. The machine includes a plurality of stations, not shown,located about the table 110 for successive cooperation with the moldingdies 12 upon rotation of the table in a predetermined direction.Specific mechanisms are provided at the stations to perform particularfunctions, in cooperation with the molding dies, required in theformation of a core, such as introducing a measured quantity of powderedmaterial into the die cavity, compressing the material to form anintegral core and ejecting the formed core from the molding die. Themolding dies are designed in a novel manner and cooperate with thestation mechanisms to provide automatic operation and high speedformation of cores. It is to be expressly understood that a number ofmolding dies greater or less than the number shown in the drawing may be7 employed, as desired.

The table 10 is provided with a plurality of circular recesses 13 formedin its upper surface, the number of circular recesses being equal to thenumber of molding dies 12. The table 10 is also provided with enlargedopenings 14 extending through its lower wall 15, an enlarged openingbeing formed in each of the circular recesses in concentric relationtherewith. As shown in FIGURE 2, the molding dies include a cylindricalbacking plate 16 positioned in a circular recess 13 and resting on itsbottom surface 17, and a circular body member 18 positioned in thecircular recess in contact with the upper surface 19 of the backingplate. The outside diameters of the backing plate 16 and the body member18 are such as to provide a snug fit between their outer peripheralsurfaces and the side walls of the circular recess. The backing plate 16includes a downwardly depending cylindrical portion 26 of reduceddiameter to freely enter 4 the opening 14 in the bottom wall #15 of thetable. The cylindrical depending portion 20 extends throughout the depthof the wall 15 and projects slightly downwardly beyond the lower surface21 of the table 11. The body member 18 extends upwardly above the uppersurface 22 of the table 11, and includes an outwardly extendingcircumferential flange 23 presenting an annular surface 24 parallel toand spaced from the upper surface 22. The circumferential flange 23cooperates with clamping devices 25 and 26 for positively retaining thebacking plate and body member of the molding dies in respective circu--lar cavities 13 of the table 10.

As shown in FIGURE 1, each of the molding dies is provided with an innerclamping device 25 lying along a radial line of the table passingthrough the center of respective molding dies and a pair of opposedouter clamping devices 26, 26 displaced approximately from therespective inner clamp 25, each of the outer clamping devices 26 beingassociated with a pair of adjacent molding dies. As illustrated inFIGURE 2, the inner clamping devices 25 include an L-shaped block 27having a leg portion 28 adapted to contact the upper surface 22 of thetable and an outwardly extending flange 29 adapted to contact a portionof the annular surface 24 of the body member, the outer edge of theflange 29 being curved to correspond to the curvature of the body member18. The block is secured in clamping position as shown by a bolt 30passing through suitable openings in the block and the table and acooperating nut 32 on the underside of the table. The outer clampingdevices 26 may be of the type shown in FIGURE 3 of the drawings. Theseclamping devices comprise a T-shaped block 33 having a central leg 34adapted to contact the table surface 22 and a pair of oppositelydisposed flanges 35 and 36 adapted to contact the annular surfaces ofadjacent body members, the outer edges of the flanges are oppositelycurved in conformance with the curvature of the side walls of the bodymembers. The block 33 is secured by a bolt 37 anchored to the table 10.With this clamping arrangement, the molding dies are secured in re--spective circular recesses and onto the table. It is to be expresslyunderstood that other types of clamping.

means may be empldyedi The body member 18 ofthe moldingdie is preferablyprovided with a centrally disposed enlarged bore 40 receiving acylindrical insert 41 comprising a single piece of carbide material. Thecircular bore 40 and the carbide insert 41 may extend throughout thedepth of the body member 18, and the carbide insert is main drawing,from the lower surface 44 of the body mem her to a plane 45perpendicular to the longitudinal axis of the bore 42 and located belowthe upper surface 46 of the body member. At the plane 45, the bore 42merges with an enlarged opening in the insert 41 extending upwardly fromthe plane 45 to the upper surface 46 of the body member. The enlargedopening is defined by a continuous internal surface 47, of circularcross-section, formed on the insert in concentric relation with thelongitudinal axis of the bore 42, and the internal surface 47 isuniformly inclined from the upper surface 46 of the body member inwardlytoward the longitudinal axis of the bore 42. In the region of theenlarged opening above the plane 45, the inclined continuous internalsurface 47 is merged with the bore 42 by a curved annular surface 48formed on the insert. The bore 43, formed in the backing plate 16 inaxial alignment with the bore 42, is of uniform diameter of the bore 42,and extends from the upper surface 19 of the backing plate downardly, asviewed in pending portion 20 in spaced relation with its lower 6 surface49. At its terminating end, the bore 43 merges with a bore 50, ofreduced diameter, extending throughout the portion 20 to the surface 49.The bore 50'is in axial alignment with the bores '42 and 43, and formsan upwardly facing annular shoulder 51 at the terminating end of thebore 43. t

The molding die further includes a cylindrical center plug or member 60'which provides the inside surface and a portion of the bottom surface ofthe pressure or molding cavity of the die, and also functions as a meansfor removing formed cores from the cavity. As shown, the center plug 60includes an intermediate cylindrical portion 61, of uniform diameter,adapted to be snugly received by the bores 42 and 43 for axial movementtherein. The center plug 60 also includes a cylindrical bottom portion62 extending downwardly from the lower end of the intermediate portioninto the bore 50 of the projection 20, the bottom portion being inconcentric relation with the longitudinal axis of the center plug. Thisconstruction presents a downwardly facing annular shoulder 63 at the endof the intermediate portion 61, the shoulder 63 being adapted to engagethe annular flange 51 and limit downward movement of the center plugrelative to the body member. The bottom portion 62 extends downwardly adistance greater than the depth of the bore 50 so that its end face 64lies in a plane displaced a slight distance below the lower surface 49of the cylindrical projection 20 when the center plug is in itslowermost position. The purpose of this arrangement will be describedmore fully below.

The center'plug is provided with a top portion 65 having a continuousexternal surface 66, of circular cross-section, in concentric relationwith the central longitudinal axis of the center plug and the bores 42and 43. The surface 66 is inclined from the upper surface 46 of the bodymember outwardly away from the longitudinal axis of the center plug. Theupper end of the intermediate portion 61 terminates in a plane 67perpendicular to the longitudinal axis of the center plug, and the lowercircular edge of the inclined surface 66 is merged with the uppercircular edge of the intermediate portion by a curved annular surface68. The

plane 67 is spaced below'the plane 45 a distance cor-.

responding to the vertical displacement between the end face 64 and thelower surface 49 of the portion 20 so that upon movement of the end face64 into the plane of the lower surface 49, the resulting upward movementof the center plug relative to the body member positions the uppercircular ends of the bore 42 and the inter-mediate portion 61 in acommon transverse plane. The inclined surface 47 of the insert 41 andthe'inclined surface 66 of the center plug 60 respectively define insideand outside concentric side wall-s of a toroidal pressure ormolding-cavity 69. The lower portions of the inner and outer side wallsand the bottom of the pressure cavity 69 are defined by the annularcurved surfaces 48 and 68.

" In FIGURE 4 of the drawings, a molding die is shown at the'pressing orcore forming station. The mechanism for effecting the core formingoperation includes a pressure device 70 located above the molding dieand a load carrying member or anvil 71 positioned below the tablebeneath the molding die. The anvil 71 is mounted independently of thetable on a foundation, not shown, suitable-for carrying the highpressure applied during the core forming operation. The upper end of theanvil comprises a cylindrical metal block 72 presentinga flat,horizontally disposed upper surface 73. The diameter of the cylindricalblock 72 may be approximately equal to the diameter of the projectingportion 20 of the backing plate 16 and is positioned with its centrallongitudinal axis aligned with the longitudinaliaxis of thec'en-ter plugwhen the molding die is properly positioned at the core forming station.The vertical position of the upper surface 73 relative to the table maybe such that the lower end face 64 of the center plug 69 is in contacttherewith, while the lower face 49 of the cylindrical projecting portion20 is spaced therefrom, upon movement of a molding die to the coreforming station, as shown in FIGURE 4. With this arrangement coreforming pressure is transmitted to the anvil independently of the tableas will appear more fully below. The pressure device includes a pressureplate or cylindrical block 75 having a centrally disposed cylindricalcavity 76 on its lower side adapted to receive a cylindrical plug 77including an integrally formed downwardly depending pressure ring 78.The plug 77 includes a horizontally disposed circumferential grove 79,lying within the cylindrical cavity 76 and receiving one end of one ormore pins, such as pin 80 carried in a horizontal bore 81 formed in thepressure plate, to. retain plug in the cylindrical cavity. The pressurering 78 is joined to the plug 77 through a tapered portion 82, andcomprises an elongated annular member including concentric inner andouter cylindrical surfaces, 83 and 84, respectively, and a terminatingannular 'end face 85 lying in a plane perpendicular to the centrallongitudinal axis of the pressure ring. The depth of the inner and outercylindrical surfaces 83 and 84 and the spacing of the surfaces 83 and 84from each other and from the central longitudinal axis of the pressurering are determined in accordance with the dimensions of the pressurecavity.

The pressure plate 75 is mounted by guide means, not shown, for movementparallel to the longitudinal axis of the center plug 60, such as.verticalmovement, and is positioned relative to the table so that thecentral longitudinal axis of the pressure ring is in axial alignmentwith the central longitudinal axis of the center plug when the moldingdie is positioned at the core forming station. A suitable pressureapplying means, such as a hydraulic system, not shown, is associatedwith the pressure plate 74 to move the pressure ring downwardly and intothe pressure cavity 68 of the molding die and applypressure required toform an integral core from powdered mag netic material. s "I T;

In FIGURE 5 the molding die and the pressure ring areillustrated intheir relative positions during a core forming operation. As shown, thepressure ring is moved to within the cavity of the molding die having amag? netic core therein formed under extremely high .pres.-: sure. Thepressure applied to the molding die is transmitted through the centerplug 60 and the body member and the projecting portion 20 of the backingplate tothe anvil 71'independe'ntly of the table 15. During the coreforming operation the end face 64 of the center plug and the lowersurface 49 of the projecting portion 20 contact the upper horizontalsurface 73 of the anvil, and the upper ends of the bore 42 and of theintermediate portion 61 of the center plug lie in a common plane 91perpendicular tothe longitudinal axis of the bore 42.

FIGURE 6 of the drawings shows a molding die at the ejector station, andFIGURE 7 illustrates the manner a formed core is ejected from themolding die.- The ejector station mechanism includes an ejector rod orplunger 95 mounted by suitable guide means, not shown, for movementparallel to the longitudinal axis of the center plug 60, and positionedwith respect to the center of rotation of the table so that its centrallongitudinal axis substan: tially coincides with the centrallongitudinal axis of the center plug when the molding die is moved tothe ejector station. Power means, not shown, is provided for applyingreciprocating movement to the plunger 95, to move the plunger betweenits non-ejecting position shown in FIGURE 6 and its ejecting positionshown in FIGURE '7. When the plunger is in the non-ejecting position,its upper end face 96 lies in a plane displaced below the plane oftheend'face 64 of the center plug when the center plug is normallypositioned relative to the body member. Upon upward movement of theplunger 95, its end face 96 contacts the lower end of the center plugand moves the center plug upwardly relative to the body member 18. Theformed core 90 moves upwardly with the center plug and is ejected fromthe pressure cavity. The stroke of the plunger is preferably such as tomove the core 90 to a position above the upper surface 46 of the bodymember for removal from the center plug by any suitable device, such asby magnetic means. Upon removal of the core the plunger is moveddownwardly to its non-ejecting position to permit movement of themolding die from the ejector station. In some cases it may be desirableto move a supporting member to beneath the core 90 when the center plugis positioned in the manner shown in FIGURE 7, and to thereafterpositively move the center plug downwardly relative to the core, by anysuitable downwardly movable means located above the center plug, notshown, in order to release the core from the center plug, the supportingmeans being operable, if desired, to deliver the core from the machine.

An enlarged sectional view of one side of the pressure cavity 69 shownin FIGURE 8 of the drawings illustrates in detail the shape of thesurfaces 47, 48, 66 and 68 and their interrelationship in defining thepressure cavity according to one embodiment of the invention. As shown,the vertical axis XX comprises the central longitudinal axis of thecenter plug 60 or the bore 43, and the axis YY is coextensive with theline of contact between the intermediate portion 61 of the center plugand the bore 42. In view of the snug fit between the center plug and thebore 42, the external surfaces of the intermediate portion 61 of thecenter plug and the internal surface of the bore 42 may be considered aslying in a cylindrical plane concentric with the axis XX, and. anyvertical section passing through the axis XX would cut the cylindricalplane along a vertical line parallel to the axis XX, such as the axisYY. The axis YY divides the pressure cavity 69 into zones 100 and 101 ofequal cross sectional area which are symmetrical with respect to theaxis YY. The bottom of the pressure cavity 69 is defined by the curvedannular surfaces 48 and 68 formed on the insert and the center plug,respectively, above the upper ends of the bore 42 and the intermediateportion 61, respectively, in concentric relation with the axis XX. Incross-section, the curved annular surfaces 48 and 68 form 90 arcs ofcircles of equal radius, i.e., arcs 102 and 103, respectively, and whenthe upper ends of the bore 42 and the intermediate portion 61 lie in thecommon plane 91, the arcs 102 and 103 form a semicircle having a centerat point 104 lying on the axis YY and in a plane Z-Z perpendicularthereto and passing through points 105 and 106 at the upper extremitiesof the arcs 102 and 103, respectively. The inclined surfaces 47 and 66of circular cross-section define, in vertical section, straight lines107 and 108, respectively, the line 107 being located on one side of theaxis YY and extending upwardly from the point 105 and being inclinedoutwardly from the axis Y--Y, and the line 108 being located on theother side of the axis YY and extending upwardly from the point 106 andbeing inclined outwardly with respect to the axis YY. Broken lines 109passing through points 105 and 106' in parallel relation with the axisXX, illustrate the equal taper of the inner and outer side Walls of thepressure cavity with respect to the axis YY.

As mentioned above one of the objects of the present invention is toprovide a novel molding die including a single piece die body capable offorming cores of compressed metallic particles of powdered material inan automatic operation. This object is accomplished, in part, by theprovision of a pressure cavity including inner and outer side wallsdefined by oppositely inclined or tapered surfaces. The feature ofproviding a pressure cavity including an outer wall surface inclinedinwardly toward the central longitudinal axis of the core permits aformed core to be removed from the cavity upon movement of the corerelative to the outside surface of the cavity in a directioncorresponding to the direction the outer wall surface of the cavitytapers away from the longitudinal axis of the core without applyingexcessive pressures to the core which would impart injury to the core.Also, the feature of providing such a cavity with an oppositely taperedinside surface makes is possible to remove the core from the center plugupon movement of the core in the same direction relative to the centerplug, i.e., in a direction corresponding to the direction the innersurface tapers toward the longitudinal axis of the core. It willtherefore be appreciated that the feature of providing a pressure cavitydefined by oppositely tapered inner and outer side walls, in combinationwith a pressure die including a single piece die body and a center plugmovably mounted relative to the die body in which the inner surface ofthe cavity is formed on the center plug and the outer surface of thecavity is formed on the die body eliminates the prior necessity ofemploying a plurality of removal die sections and makes it possible toform cores of compressed powdered material in an automatic operation. Inparticular, after the core forming pressure is applied and the pressurering moved to its retracted position, the center plug may be movedrelative to the die body in a direction corresponding to the directionthe outer surface of the cavity tapers away from the longitudinal axisof the core, upwardly as viewed in the drawings, to move the formed corerelative to the die body and out of the cavity defined by the wall ofthe die body. Thereupon, the core may be moved relative to the centerplug in a direction corresponding to the direction the inner surface ofthe pressure cavity tapers toward the longitudinal axis of the core, tomove the core from the center plug. The latter operation may beaccomplished in a number of ways such as by inserting a cradle beneaththe core when positioned as shown in FIGURE 7 and then applying adownward force on the center plug of a magnitude necessary to terminatecontact between the core and the center plug. By providing the surfacesdefining the pressure cavity with a thin film of lubricating oil thecores may be easily removed from the pressure cavity upon application ofpressures of a relatively low order of magnitude materially less thanthe magnitude of pressures that may impart damage to the core. Thedegree of taper of the inner and outer side walls is shown exaggeratedin the drawings for the purpose of clarity. In actual practice it hasbeen found that a taper of the order of one degree is adequtae for theinner and outer side walls of a pressure cavity designed for formingmagnetic cores. It is to be expressly understood that tapers in excessof one degree may be employed if desired. In addition, the feature ofemploying a pressure cavity defined by oppositely inclined concentricinner and outer surfaces permits the pressure cavity to be reformed tocompensate for wear. The surfaces of pressure cavity which contactpowdered metallic material, especially when under high pressure, thatis, the surfaces of the cavity which define the formed core, are subjectto wear due to abrasive action of the powdered particles, and eventuallythe cavity size will change and cores of the desired dimensions cannotbe obtained. With a pressure cavity of the character provided by thepresent invention, it is possible to reform the lower portion of thepressure cavity by merely extending the depth of the pressure cavity inaccordance with a predetermined shape. This feature eliminates thedisadvantage of prior molding dies in which the bottom face of the diebody as well as the contacting surfaces of the die sections are requiredto be ground in order to compensate for wear of the surfaces definingthe cavity.

The novel feature provided by the present invention of forming apressure cavity composed of two zones and 101 which are symmetricalabout the axis YY,

results in equal distribution of the core forming pressure to the centerplug and the body member and assures substantially uniform applicationof pressure to the core. This arrangement provides a core of maximumstrength and improved uniform density characteristics. The furtherfeature of defining the bottom portion of the pressure cavity bycooperating curved annular surfaces which are symmetrical with respectto the axis Y--Y, insures substantially equal distribution of forcesthroughout the core and minimizes development of localized stresses inthe core structure.

In the formation of magnetic cores pressed from insulated particles ofmagnetic material under extremely high pressure it has been found thatthe presence of air trapped in the powdered material may have adisadvantageous eifect upon the properties of the formed core, dependingupon the permeability of the core, which is determined, for the mostpart, by the size of the par,- ticles and the thickness of theinsulation. In the formation of low permeability cores by compressingheavily insulated and finely divided particles of magnetic material, itis believed that trapped air collects in the powdered material adjacentthe lower surface of the pressure ring and prevents the formation of thepowdered material in this region into an integral mass with theremaining portion of the powdered material. It has been found that thisphenomenon results in the formation of cores which are weak at its endwhich contacts the pressure ring during the forming operation, andfrequently the outer surface of the core at this end will split from themain body of the core. The present invention provides a novelarrangement for overcoming this problem. As shown in FIGURE 9, the innerand outer annular edges of annular end face 85 and the lower edges ofthe cylindrical inner and outer side walls 83 and 84 are joined togetherby annular curved surfaces 110 and 111, respectively. When a pressurering shaped in this manner is moved downwardly into a pressure cavityand into pressure contact with a charge of powdered material, a portionof the powdered material including trapped air is forced outwardly.toward the inner and outer surfaces of the cavity and collects inupstanding circumferential, recesses located between the inner surfaceof the cavity and the inner curved annular surface 110 of the pressurering, and between the outer surface of the cavity and the outer curvedannular surface 111 of the pressure ring. As shown in FIGURE 10, a coreformed with the type of pressure ring described above, includes innerand outer circumferential upstanding lips 112 and 113 which are ofdifferent density and are relatively weak with respect to the remainingportion of the core comprising an integral mass substantially free oftrapped air. After the core is removed from the molding die, thecircumferential lips 112 and 113 may be removed by a simple grindingoperation at which time the inner and outer concentric edges of the coreat its upper end may be rounded, such as at 114 and 115, to provide acore as shown in FIGURE 11. It hasbeen determined that in the formationof cores of high permeability, requiring lightly insulated, coarseparticles of magnetic material, the strength of the core is not affectedby the presence of air that may be trapped in the powdered materialduring the core forming operation, and that a pressure ring having theinner and outer annular edges of its end face 85 lying in the plane ofthe side walls 83 and 84, respectively, may be employed, such as apressure ring of the shape illustrated in FIG- URE 4. In actualoperations it has been determined that magnetic cores of a permeabilityof the order of 125 may be formed with a pressure ring having an endface shaped in the manner shown in FIGURE 4, while magnetic cores of apermeability of 60 or less should be formed with a pressure ring of thecharacter illustrated in FIGURE 9.

As shown in FIGURES L1, 12 and 13, a core formed of pressed powderedmagnetic material employing the principles of the present inventionincludes substantially perfec-tly circular, concentric inner and outerwall surfaces 116 and 117, which are continuous and substantiallysmooth, and continuous top and bottom surfaces 118 and 119 which mergesmoothly, without surface interruptions, such as grooves or raisedportions, into the side wall surfaces. In addition, the core is ofsubstantially uniform density transversely of the section, that is, inany section of the core lying in a plane perpendicular to thelongitudinal axis of the core, the core structure is of substantiallyuniform density. With this construction the outer circumferentialmarginal portion of the core, including its outer circumferentialsurfaces, will be of uniform density. A magnetic core having theforegoing characteristics possesses improved magnetic, electrical andmechanical properties as compared to corresponding properties of coresproduced according to prior art teachings.

According to the preferred embodiment of the invention, the body member18 includes an insert 41 comprising a single piece of carbide materialand the center plug 61) and pressure'ring 78 may also be formed ofcarbide material. In order to obtain cores of compressed particles ofmetallic material having substantially uniform density characteristicsas described above, it is necessary to provide a super finish on thecore defining surfaces. It has been found that carbide material, such astungsten carbide, is capable of receiving a super finish which ismaintained throughout a large number of core forming operations in spiteof the highly abrasive action of the particles of metallic material.Also, it is believed carbide material has a lower coefficient offriction, as compared to steel die surfaces employed heretofore, whichaids in the removal of formed cores from the pressure cavity. In theprior molding dies including a plurality of arcuate die sections it wasnot possible to employ a carbide insert to define the outer contour ofthe pressure cavity since the inherent flexure of the die sections wouldbreak the carbide material.

Another form of cavity construction is shown in FIG- URE 14 of thedrawings. As shown, the outer and inner walls of the cavity are formedby tapered surfaces 107 and 108, respectively, and the bottom of thecavity includes a flat surface having its edges merged with curvedsurfaces 126 and 127 which in turn merge with the lower edges of theouter and inner side walls, respectively. This type of cavityconstruction has particular utility in connection with the formation ofcores having relatively large spacing between the inner and outer wallsurfaces. In the cavity structure shown in FIGURE 14 and in FIGURE 8 thedividing line between the center plug and the body member lies along aline which intersects the bottom of the cavity at the point of tangencythereon with a plane perpendicular to the longitudinal axis of thecavity. In FIGURE 8, in which the bottom of the cavity is formed by acurved surface, which in section defines a semi-circle, there exists onepoint of tangency on the bottom surface with a plane perpendicular tothe longitudinal axis of the cavity, and the dividing line between thecenter plug and the die body coincides with the axis Y-Y. In FIGURE 14,however, there exist two points of tangency and the dividing linebetween the center plug and the die body preferably passes through thepoint of tangency adjacent the outer wall of the cavity. Although in theform of pressure cavity of the character shown in FIGURE 14 the dividingline may be displaced from the position shown inwardly toward thelongitudinal axis of the cavity, location of the dividing line as shownin this figure and also as shown in FIGURE 8 provides the maximum areaof contact between the for-med core and the center plug for theparticular type of cavity without presenting difficult problems thatwould exist if the dividing line was displaced outwardly from theposition shown in FIGURE 14 or inwardly or outwardly from the positionshown in FIGURE 8. Inasmuch as a greater area of the core contacts theouter surface of the cavity than the area of the core that contacts theinner surface of the cavity, more pressure will be required to move thecore relative to the die body than will be required to move the corerelative to the center plug. Consequently, the feature of forming thecenter plug to provide the fiat surface 125 of the bottom of the cavityprovides the maximum permissible area of contact between the core andthe center plug and makes it possible to apply forces of the necessarymagnitude to remove the core from the die body without imparting injuryto the core.

In operation, the table 10 is rotated in a predetermined direction tosuccessively move the molding dies 12 to a charging station, thepressing station and the ejector station, in the order named. At thecharging station a mechanism is provided for introducing a predeterminedquantity of powdered material into the pressure cavity, the quantity ofthe charge depending upon the size of pressure cavity. When a moldingdie is located at the charging station the center plug 60 is positionedrelative to the body member 18 as shown in FIGURE 2. Before the chargeof powdered material is introduced into the pressure cavity, thesurfaces defining the pressure cavity are coated with a suitablelubricating material. A separate station, preceding the filling station,may be provided for this operation. After the pressure cavity ischarged, the table is rotated to position the molding die at thepressure or core forming station in proper relation with the anvil 71and the pressure ring 78 as shown in FIGURE 4. Thereupon the pressureplate 75 is moved downwardly to move the pressure ring into the cavityin contact with the charge of powdered material and the requiredpressure is applied to form an integral core, such as a pressure of200,000 to 250,000 pounds per square inch. FIGURE shows the relativepositions of the pressure ring and molding die during the core formingop eration. The applied pressure is equally distributed between thecenter plug and the body member, due to the design of the pressurecavity, transmitted independently to the anvil, without loading thetable. Following the core forming operation the pressure is relieved andthe pressure ring removed from the cavity. Thereupon the table isrotated to move the molding die to the ejector station shown in FIGURE6. After location at this station, the plunger 95 is moved upwardly intothe bore 43 to move the center plug 60 upwardly relative to the bodymember, as shown in FIGURE 7. The formed core 90 moves upwardly with thecenter plug and is removed from the opening provided in the insert 41.When the center plug is in its ejecting position the core 90 mayberemoved therefrom by applying upward movement to the core relative tothe center plug. The core 90 may also be removed by placing a supportbeneath the core and applying a downward force on the center plug. Thesupport may thereafter function as a means for delivering the core fromthe machine. The center plug is then retracted to its normal positionand the molding die in a condition to 'be moved to the charging stationto receive another charge of powdered material and proceed through thesequence of operations described above.

The principles of the present invention may be employed to form bodiesfrom powdered material, especially in cases where extremely highpressures are required, such as bodies of powdered carbonyl or reducediron or magnetic cores of insulated particles of magnetic material ofhigh permeability such as Permalloy, flakenol or alfenol, for example.In the formation of magnetic cores of compressed insulated particles ofmagnetic material according to the present invention, the novel featuresdescribed above which result in application of uniform pressure to thecore during its formation and the production of a core of substantiallyuniform density, also insures that the effectiveness of the insulationof the magnetic particles is not impaired and that the core possessessubstantially uniform insulation effectiveness. Thus cores of compressedinsulated particles of magnetic material formed according to theprinciples of the present invention exhibit relatively low eddy currentlosses when incorporated in a coil.

There is thus provided by the present invention a novel magnetic core ofcompressed insulated particles of magnetic material which possessesimproved magnetic, electrical and mechanical characteristics as comparedto magnetic cores produced by following prior methods and ap paratus.The core may be of toroidal shape, of substantially perfect circularcross-section having concentric inner and outer side walls and includessubstantially smooth, continuous surfaces. The present inventionprovides a novel molding die structure for use in forming cores ofpowdered material requiring application of relatively high pressure. Thenovel molding die structure is characterized by a single block ofmaterial presenting a continuous surface defining the outer contour of apressure cavity. This feature makes it possible to form cores of a shapesubstantially corresponding to the shape of the pressure cavity, such ascores of substantially circular cross section having concentric innerand outer side walls. The pressure cavity of the novel molding die isformed in part by a center plug and is designed in such a manner as topermit removal of a formed core from the cavity upon movement of thecenter plug and overcomes prior core removal difiiculties which requiredthe use of a plurality of arcuate die sections and makes it practicableto form cores by an automatic operation.

Although several embodiments of the invention have been disclosed anddescribed herein, it is to be expressly understood that various changesand substitutions may be made therein without departing from the spiritof the invention as well understood by those skilled in the art.Reference therefore will be had to the appended claims for a definitionof the limits of the invention.

What is claimed is:

1. Molding apparatus comprising a body member including a single pieceof rigid material having a top surface and a bottom surface and anopening therethrough defined by a continuous internal wall of circularcrosssection extending through the body member from the top surface tothe bottom surface,

the internal wall including a lower part and an upper part,

the lower part of the internal wall extending from the bottom surface ina direction toward the top surface and including a constant diameterportion having a terminating end lying in a plane perpendicular to thecentral axis of the opening and located intermediate the top surface andthe bottom surface,

the upper part of the internal wall extending from the top surface in adirection toward the bottom surface and including a first portion and asecond portion, the first portion of the internal wall being taperedwith its diameter decreasing in a direction from the top surface towardthe bottom surface and terminating in a small diameter end having aradius greater than the radius of the constant diameter portion andlying in a plane perpendicular to the central axis and spaced from theplane of the terminating end of the constant diameter portion of theinternal wall,

the second portion of the internal wall extending from the smalldiameter end of the internal wall to the terminating end of the constantdiameter portion of the internal wall and including a concave surfaceextending from the small diameter end of the internal wall in adirection toward the bottom surface and inwardly toward the central axisand terminating in the plane of the terminating end of the constantdiameter portion of the internal wall,

an elongated member positioned in the opening of the body member,

the elongated member including a continuous external Wall of circularcross-section having a lower part and an upper part, the lower part ofthe external wall being of constant diameter for snug sliding engagementwith the constant diameter portion of the internal Wall to position theelongated member in the opening of the body member with the longitudinalaxis of the elongated member coincident with the central axis of the Iopening,

the constant diameter portion of the external wall having a terminatingend lying in a plane perpendicular to the longitudinal axis and locatedintermediate the ends of the elongated member,

the upper part of the external wall including a first portion and asecond portion, the first portion of the external wall being taperedwith its diameter increasing in a direction toward the lower part of theelongated member and terminating in a large diameter end having a radiusless than the radius of the lower part of the external wall and lying ina plane perpendicular to the longitudinal axis and spaced from the planeof the terminating end of the constant diameter portion of the externalwall, the second portion of the external wall extending from the largediameter end of the external wall to the terminating end of the constantdiameter portion of the external wall and including a concave surfaceextending from the large diameter end of the external wall in adirection toward the lower part of the external wall and away from thelongitudinal axis and terminating in the plane of the terminating end ofthe constant diameter portion of the external wall,

the upper part of the internal wall and the upper part of the externalwall defining a pressure cavity upon the elongated member and the bodymember being relatively positioned with the terminating end of theconstant diameter portion of the external wall and the terminating endof the constant diameter portion of the external wall lying in a commonplane, and a pressure ring mounted above the body member for movement ina direction toward the top surface of the body member and into thepressure cavity.

2. A molding apparatus as defined in claim 1 in which the upper part ofthe internal wall and the upper part of the external wall are formed ofcarbide material.

3. A molding apparatus as defined in claim 1 in which the upper part ofthe external wall and the upper part of the internal wall aresymmetrical with respect to an imaginary cylindrical surface concentricwith the central axis of the opening of the body member and bisectingthe pressure cavity.

4. A molding apparatus as defined in claim 3 in which the concavesurface of the second portion of the internal wall extends to theterminating end of the constant diameter portion of the internal walland in which the central axis of the constant diameter portion of theinternal wall is perpendicular to a plane in tangential relation withthe concave surface of the internal wall.

5. A molding apparatus as defined in claim 4 in which the concavesurface of the second portion of the external wall extends to theterminating end of the constant diameter portion of the external wall,

in which the constant diameter portion of the external wall isperpendicular to a tangent of the concave surface of the external wall,

and in which the imaginary cylindrical surface is coincident with theengaging surfaces of the constant diameter portions of the internal walland the external wall.

.6. A molding apparatus as defined in claim 4 in which the secondportion of the external wall includes an annular surface lying in aplane perpendicular to the longitudinal axis,

in which the concave surface of the external wall extends to the smalldiameter edge of the annular surface,

and in which the large diameter edge of the annular surface is at theterminating end of the constant diameter portion of the external wall.

7. A molding apparatus as defined in claim 1 including means positioningthe terminating end of the constant diameter portion of the internalwall and the terminating end of the constant diameter portion of theexternal wall in a common plane.

8. A molding apparatus as defined in claim 1 in which the pressure ringincludes a hollow cylindrical member having a cylindrical internalsurface and a cylindrical external surface concentric with thelongitudinal axis of the elongated member,

a flat annular end face lying in a plane perpendicular to thelongitudinal axis,

a convexly curved circumferential edge extending between the outercircular edge of the annular end face and the cylindrical externalsurface,

and a convexly curved circumferential edge extending between the innercircular edge of the annular end face and the cylindrical internalsurface.

9. A molding apparatus as defined in claim 1 including a supportingmeans for the body member having a first side in contact with the bottomsurface of the body member,

the supporting means having an opening for the elongated member,

and anvil means in contiguous relation with the second side of thesupporting means and in contact with the elongated member.

10. A molding apparatus as defined in claim 9 in which the second sideof the supporting means is spaced a predetermined distance from theanvil means,

in which planes passing through the terminating ends of the constantdiameter portions of the lower part of the internal wall and the lowerpart of the external wall are spaced a distance equal to thepredetermined distance,

and in which the supporting means is movable in a direction toward theanvil means into contact with the anvil means to position theterminating ends of the constant diameter portions of the internal walland external wall in a common plane.

References Cited in the file of this patent UNITED STATES PATENTS1,305,975 Pfanstiehl June 3, 1919 1,600,828 Latour Sept. 21, 19261,855,855 Gillis et al Apr. 26, 1932 1,858,225 Frederick May 10, 19321,974,056 Schrell Sept. 18, 1934 2,093,029 Bolk Sept. 14, 1937 2,218,669Whipple Oct. 22, 1940 2,282,155 Bandur May 5, 1942 2,449,515 Seelig'Sept. 14, 1948 2,495,064 Horvath Jan. 17, 1950 2,536,689 Kress et a1Jan. 2, 1951 2,558,823 Crowley et a1 July 3, 1951 2,562,876 Baeza Aug.7, 1951 2,583,441 Dalmer Jan. 22, 1952 2,798,255 Winters July 9, 19572,800,684 Luthman July 30, 1957 2,841,822 Clough et al July 8, 1958FOREIGN PATENTS 1,082,839 France June 23, 1954

